Lecture27第六章等效电路影响阈值电压的因素

1、 micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui provincemosfetmosfet特性分

2、析特性分析 micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui provinceoutline1.

3、1. 等效电路和频率响应等效电路和频率响应2. mosfet2. mosfet的类型的类型3. 3. 影响阈值电压的其他因素影响阈值电压的其他因素 （1 1）掺杂浓度和氧化层厚度）掺杂浓度和氧化层厚度 （2 2）衬底偏置）衬底偏置 micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui pro

4、vince micro electromechanical system research center of engineering and technology of anhui provincemosfetmosfet的小信号特性是指在一定工作点上，输出端电流的微小的小信号特性是指在一定工作点上，输出端电流的微小变化与输入端电压的微小变化之间有定量关系。这是一种线性变化与输入端电压的微小变化之间有定量关系。这是一种线性变化关系，可以用线性方程组描述小信号特性，其中不随信号变化关系，可以用线性方程组描述小信号特性，其中不随信号电流和信号电压变化的常数即小信号参数。电流和信号电压变化的常数即

5、小信号参数。 micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province在线性区的电阻称为

6、开态电阻或导通电阻，可表示为：在线性区的电阻称为开态电阻或导通电阻，可表示为：2)(2dthgn0dvvvvlzcid)(thg0ndlvvlzcg常数gvdddlvig)(1thg0ndlonvvzclgr可忽略可忽略 micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province

7、 micro electromechanical system research center of engineering and technology of anhui province在在vds较小时，较小时，gdl与与vds无关。随着无关。随着vds的增大，但还未到的增大，但还未到饱和区，饱和区，gdl将会减小。此时有：将会减小。此时有：不可忽略不可忽略常数gvdddlvig)(dthg0ndlvvvlzcg micro electromechanical system research center of engineering and technology of anhui pro

8、vince micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro ele

9、ctromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province在不考虑沟道长度调变效应时，在不考虑沟道长度调变效应时，ids与与vds 无关。无关。饱和工作区的饱和工作区的gds为零，即输出电阻为无穷大。为零，即输出电阻为无穷大。0dsg常数gvdddsvig2thgn0dsat)(2vvlzci m

10、icro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province理想情况下，对于任何超过夹断条件的

11、漏极电压，漏极电流理想情况下，对于任何超过夹断条件的漏极电压，漏极电流为常数（电流与电压无关）。即对于为常数（电流与电压无关）。即对于vdvdsat时的情况，漏极时的情况，漏极电阻为无限大。饱和区漏极电阻定义为：电阻为无限大。饱和区漏极电阻定义为：常数gvdsatdsatdsivr micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering a

12、nd technology of anhui province micro electromechanical system research center of engineering and technology of anhui province对于实际对于实际mosfet，饱和区输出特性曲线总有一定的倾斜，饱和区输出特性曲线总有一定的倾斜，使输出电导不等于零，即输出电阻不为无穷大。使输出电导不等于零，即输出电阻不为无穷大。dsatathdssdsatddsatdsat)(2/iqnvvvllixlllliigs常数gvddsatdsvigathdss21thdsasdsatds)(2)

13、(2qnvvvlvvvqniggsgs当当(vgs-vth)增大时，增大时，gds增大。当增大。当vds增加时，增加时，gds也增大，使输出电阻下降。也增大，使输出电阻下降。 micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanica

14、l system research center of engineering and technology of anhui province常数dvgdmlvig2)(2dthgn0dvvvvlzciddvlzcgn0ml2thgn0dsat)(2vvlzci常数dvgdmsvig)(thgn0msvvlzcg micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center

15、 of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui provincezlogcccgscgd栅极栅极- -源极、漏极两个源极、漏极两个n+n+区的区的重叠部分；源极衬底；栅极重叠部分；源极衬底；栅极衬底；漏极、源极两个衬底；漏极、源极两个pnpn结结之间的电容之间的电容cds micro electromechanical system research center of en

16、gineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province 对跨导的影响对跨导的影响由于由于mosfet源区的体电阻、欧姆接触及电极引线等附加电源区的体电阻、欧姆接触及电极引线等附加电阻的存在，

17、使源区和地之间有一个外接串联电阻阻的存在，使源区和地之间有一个外接串联电阻rs：如果如果rsgm很大：很大：串联电阻（起负反馈作用）不能忽略时：串联电阻（起负反馈作用）不能忽略时：sdsgsgsrivvmsmm1grggsmsmmsmm11rgrggrgg常数dvgdmlviggsvgsvdsisr micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engi

18、neering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province若漏区的外接串联电阻为若漏区的外接串联电阻为rd ，在线性工作区受，在线性工作区受rs 及及rd 影响影响的有效输出电导：的有效输出电导：1、rs 和和rd会使跨导和输出电导变小；会使跨导和输出电导变小；2、在设计和制造、在设计和制造mosfet时应尽量减少漏极和栅极串联电阻。时应尽量减少漏极和栅极串联电阻。说明：说明：ddsd

19、d)(1grrgg常数gvdddlvig micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui pro

20、vince可得：可得：移项得到：移项得到：dssggsddssdds)(irvvirrvvgmdddlvgvgiddssddssgmd)()(dlirrvgirvgisddsmssgdsmsmddldldl)(1)(1vgrrgrgvgrrgrgi代入代入根据：根据：mgdlg串联电阻的导纳变化串联电阻的导纳变化 micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center

21、of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province截止频率截止频率f0定义为定义为mosfet的输入电流和输出电流相等时的频的输入电流和输出电流相等时的频率，即器件输出短路时，器件不能够放大输入信号时的频率。率，即器件输出短路时，器件不能够放大输入信号时的频率。gsggsgdgsinv)c(2v)cc(2zlffioxgcczl式中，总的栅电容总的栅电容gsmou

22、tvgi)( 2c2dsatd2dngm0vvlvgf 2)(c22thgngm0lvvgf micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering a

23、nd technology of anhui province1、对于、对于n沟道沟道mosfet，在，在vgs=0时，不存在沟道，只有当时，不存在沟道，只有当vgsvth时，栅极下才感应导电沟道，这种时，栅极下才感应导电沟道，这种mosfet通常称通常称为为n沟道增强型（常闭型）。沟道增强型（常闭型）。2、在、在vgs=0时，表面已形成反型导电沟道，器件处于导通状时，表面已形成反型导电沟道，器件处于导通状态，称为态，称为n沟道耗尽型（常开型）。要使沟道耗尽型（常开型）。要使n沟道耗尽，必须在沟道耗尽，必须在栅极上施加一定的负电压。栅极上施加一定的负电压。 micro electromecha

24、nical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system re

25、search center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province根据：根据：si0b00mssi0bfbthcqcqcqvvfassiasdmab42nqnqxq

26、nq(6-9-1)(6-9-1) micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui provinc

27、e micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province（1 1）离子注入法：由于用

28、离子注入掺杂含量可以非常精确，）离子注入法：由于用离子注入掺杂含量可以非常精确，所以能精确的控制阈值电压。所以能精确的控制阈值电压。 micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research cen

29、ter of engineering and technology of anhui province（2）改变氧化层的厚度。这种方法广泛应用于）改变氧化层的厚度。这种方法广泛应用于mosfet之间之间的隔离。这时，氧化层厚度比源漏区之外的氧化层（场区氧化的隔离。这时，氧化层厚度比源漏区之外的氧化层（场区氧化层）薄得多。于是场区氧比层层）薄得多。于是场区氧比层vth比栅氧化层的比栅氧化层的vth大得多。大得多。若将适当栅偏压同时加在栅极氧化层和场区氧化层上，栅下形若将适当栅偏压同时加在栅极氧化层和场区氧化层上，栅下形成了反型沟道，而场区氧化层下面的半导体表面仍保侍耗尽状成了反型沟道，而场区氧化

30、层下面的半导体表面仍保侍耗尽状态。态。 micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui prov

31、ince当有一反向偏压加在衬底和源之间当有一反向偏压加在衬底和源之间(对于对于n沟道，加在沟道，加在p衬底上的衬底上的电压电压vsb相对于源为负相对于源为负)时，耗尽层将加宽，使得空间电荷层中时，耗尽层将加宽，使得空间电荷层中负的固定电荷负的固定电荷qb增加：增加：增加固定电荷的增加固定电荷的qb：2/1siasdab)2(nqxqnq(6-9-2)2/1sibsasb)(2vnqq(6-9-3)()2(2/1si2/1sibs2/1asbvnqq(6-9-4) micro electromechanical system research center of engineering and technology of anhui province micro electromechanical system research center of engineering and technology of anhui prov